The present invention relates generally to the art of joining conduits such as plastic pipes together and, more particularly, to the art of converting a mechanical joint to a fusion joint. The invention will be described in connection with a tapping tee for a plastic natural gas main, but those of ordinary skill in the art will quickly recognize that the invention has broader application to other systems including but not limited to plastic pipe unions, elbows, tees, and in-line connectors.
Tapping tees are generally known in the art and used to provide structure for tapping into a gas main so that gas can be conducted from the main to a home or business. One example of a tapping tee, known as a saddle fusion tapping tee, is shown generally at 10 in FIGS. 1 and 2. The fusion tapping tee 10 is typically formed of plastic and includes an arcuate portion 12 that has a radius approximating the outside radius of the gas main. The tapping tee 10 is designed to be secured to the main by heating the arcuate surface 12 with a heating iron along with a portion of the external surface of the gas main. Once heated, the heating iron is removed and the wall defining the arcuate surface 12 is caused to be brought into contact with the heated gas main where a fusion of the main and the tee occurs.
The tee includes a branch 14 to which a service line 16 extending from a home or business is connected for communication with the main. The service line 16 is interconnected with the branch 14 by means of a mechanical coupling 18 which provides a quick and convenient manner of coupling the service line to the tapping tee in the field.
The mechanical coupling 18 is typically secured to the branch 14 of the tee by a butt fusion joint 20. Often the tee 10 is fused with the mechanical coupling 18 by the manufacturer to simplify the coupling with the service line 16 in the field, although alternatively the mechanical coupling may be fused to the tee by the user. Mechanical couplings 18 adapted for butt fusion joints typically include a body having a plastic end surface (35 as shown in FIG. 3). The butt fusion joint 20 is made using a heating iron which heats the end surface of the branch 14 and the end surface 35 of the mechanical coupling 18. Once heated until the plastic softens, the heating iron is removed and the two elements are brought into engagement where a fusion bead is created as the elements cool.
One example of a mechanical coupling 18 is the stab-type coupling manufactured by Perfection Corporation and sold under the trademark PERMASERT®, which is shown in U.S. Pat. No. 5,429,025 to Volgstadt commonly assigned to the same assignee as the present invention. A stab-type coupling enables a pipe, such as the service line 16, to be coupled simply by thrusting the pipe into a cavity of the coupling where both a sealing and gripping action occurs on the exterior surface of the pipe.
As shown in FIG. 3, the pipe 16 is shown thrust into the coupling 18 until the free end 20 engages a radial wall 22 of the stiffener 24. Gripping of the pipe 16 provided by a collet 26 having ramped teeth 28. The collet 28 has the capability of expanding, and the dimensions of the pipe 16 and the collet are such that as the pipe is thrust through the collet, the collet will cause to be expanded a slight amount. Any attempted withdrawal of the pipe produces a “Chinese finger” effect as the frusto-conical surface 30 of the collet 28 is caused to engage a molded-in backup ring 32 of the coupling body 34. Attempted withdrawal, therefore, causes the collet 28 to be brought into tight fitting engagement with the external surface of the pipe 16. O-rings 36, 38 encircling the external surface of the inserted pipe 16 seal the pipe against leaks.
The coupling 18 also includes a retaining ring 42 having a plurality of teeth 44 for engaging the external surface of the pipe. The retaining ring 42 provides for additional retention of the pipe 16 in the coupling 18 upon attempted withdrawal. When the pipe 16 is attempted to be withdrawn from the coupling 18, the retaining ring 42 will be caused to move to the right of FIG. 3 causing the remaining elements to “stack up.” This action brings the collet 26 into firm engagement with the backup ring 32 to provide for additional holding or gripping of the pipe 16. From the description above, it is apparent that once the service line 16 is installed in the mechanical stab-type coupling it cannot be withdrawn.
In a normal installation, the tapping tee 10 is secured to a gas main and the service line 16 is stabbed into the mechanical coupling 18. After securing the service line 16 to the main, a hole is drilled in the main whereby gas is permitted to flow into the tapping tee and into the service line. A pressure test is then run to determine whether there is any leakage at either the fusion joint between the tee and the main or at the mechanical coupling 18.
In the event that a leak should be found in the mechanical coupling 18, there is no effective way to repair the coupling since the internal components are not accessible. Indeed, in some cases, the leak is caused not by a problem with the mechanical coupling as such, but rather the presence of a score line on the pipe 16 which prevents effective sealing of the external surface of the pipe by the internal O-rings 36 and 38 of the coupling. Since there is no effective way to gain access to the sealing components of the mechanical coupling 18 and since it is not possible to withdraw the pipe 16 once inserted, a leak will normally require scrapping of the entire installation.
In light of the foregoing specifically noted deficiencies and others associated with conventional tapping tees and methods, it has been deemed desirable to provide a new and improved tapping tee and method that overcome these deficiencies and that provide better overall results.